1. Field of the Invention
The invention relates to a voltage equalizer for a battery assembly, and more particularly to a voltage equalizer that balances voltages among multiple battery units of the battery assembly by a relatively simple circuit configuration.
2. Description of Related Art
Batteries are often connected in series or parallel to form a battery assembly according to different applications as demanded. When the batteries are connected in series as a battery string, a charging current flowing through each of the batteries of the battery string is identical. Because of manufacturing material, manufacturing processes, operating environment, operating temperature, etc., each battery may differ from others in voltage or power capacity. Therefore, some of the batteries may be over charged while others are insufficiently charged. A battery voltage is usually used as an important factor to determine the charging status of a battery. When a battery has been over charged, the charging power applied to the battery will transform into heat energy to increase temperature of the battery assembly. Thus, life of the battery assembly will be reduced significantly and each battery may be subjected to a permanent damage. Therefore, a voltage equalizer is necessary to protect each battery from being over charged.
The conventional voltage equalizers may comprise different types described hereinafter.
1. Zener diode-based voltage equalizer: With reference to
2. Resistor-based voltage equalizer: With reference to
3. Inductor-based voltage equalizer: With reference to
4. Capacitor-based voltage equalizer: With reference to
For most of the above-mentioned voltage equalizers, each battery has to cooperate with a switch. Because the voltage equalizer is comprised of a large number of electronic components, the reliability of the voltage equalizer will be decreased. For example, if a battery string is composed of N batteries connected in series, N switches or N−1 inductors are required. Furthermore, N pulse-width-modulation (PWM) signals are applied to respectively control the N switches.
The main objective of the present invention is to provide a voltage equalizer to balance voltages among multiple battery units by a relatively simple circuit configuration. Further, the cost and complexity of the voltage equalizer can be reasonably reduced. In another aspect, the voltage equalizer will provide superior reliability.
The voltage equalizer in accordance with the present invention has a transformer, a switch and a controller. The transformer has a primary winding connected to the battery assembly and the controller through the switch, and further has multiple secondary windings connected to the battery units respectively. When the switch is alternately turned on and off, the transformer draws energy from the battery units with the higher voltage and couples the energy to the secondary windings to charge the battery unit with the lower voltage for balancing the voltages of the battery units.
Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
With reference to
The fly-back transformer T1 comprises a primary winding 11 and multiple secondary windings 12-15. The number of the secondary windings 12-15 is the same as the number of the battery units B1-B4. The primary winding 11 has a first end and a second end, wherein the first end is connected to one end of the battery assembly 100, and the second end is connected to the switch 20. Each of the secondary windings 12-15 is connected across a respective battery unit B1-B4 through a forward-direction diode D1-D4.
In more detail, each of the secondary windings 12-15 has a first end and a second end. The first ends of the secondary windings 12-15 are connected to anodes of the multiple diodes D1-D4 respectively. The second end of the last secondary winding 15 is connected to ground while the second ends of other secondary windings 12-14 are connected to cathodes of the subsequent diodes D2-D4 respectively. The cathodes of the forward-direction diodes D1-D4 are further respectively connected to the battery units B1-B4.
The switch 20 is connected between the second end of the primary winding 11 and the ground and has a control terminal. The switch 20 may be a MOS transistor having a gate as the control terminal.
The controller 30 detects a voltage V1-V4 across each battery unit B1-B4 and is connected to the control terminal of the switch 20. The controller 30 outputs a switching signal VG to turn on or off the switch 20.
With reference to
1. When the battery units B1-B4 are charged and the controller 30 is activated and detects the occurrence of inconsistent voltages V1-V4 among the battery units B1-B4, i.e. the voltage V1-V4 of any battery unit B1-B4 is different from others, the controller 30 outputs the switching signal VG to the switch 20. When the switch 20 is turned on during the high level periods of the switching signal VG, the fly-back transformer T1 draws energy from the battery assembly 100. Therefore, a current flows through the primary winding 11. Because the battery units B1-B4 are connected in series and a current flowing through the battery units B1-B4 is the same, the fly-back transformer T1 draws more energy from the battery unit B1-B4 having a higher voltage V1-V4 and draws less energy from the battery unit B1-B4 having a lower voltage V1-V4. A maximum voltage (VP) detectable from the primary winding 11 will be the sum total of the voltages V1-V4 of all battery units B1-B4.
2. When the switch 20 is turned off during the low level periods of the switching signal VG, polarities on the primary winding 11 and on the secondary windings 12 will be reversed, and the energy stored in the primary winding 11 will be coupled to the secondary windings 12-15 to induce a charging current. As an example, if the second battery unit B2 has the lowest voltage V2, the second diode D2 connected to the second secondary winding 13 will be conducted firstly prior to other diodes. Because all the secondary windings 12-15 have the same number of coil turns, voltages of each secondary winding 12-15 is limited to V2 (ignoring a forward conduction voltage of the diode D2). Only the second secondary winding 13 has a charging current IS2 for charging the second battery unit B2. The second diode D2 ensures the flowing direction of the charging current IS2 from the secondary winding 13 to the second battery unit B2. Since other secondary windings 12, 14 and 15 have no charging current, the voltage V2 of the second battery unit B2 will rise gradually.
3. After a period T of operation time, the voltages V1-V4 of all battery units B1-B4 will be substantially equivalent. The controller 30 stops its operation to reduce power consumption of the battery units B1-B4.
4. The period T of operation time may be a default constant period or determined by the controller 30 according to the voltages V1-V4 of the battery units B1-B4.
The voltage equalizer of the present invention uses fewer electronic components to achieve the objective of voltage balancing, particularly only using one single switch 20. The number of the secondary windings 12-15 is the same as that of the battery units B1-B4. Therefore, the cost and complexity of the voltage equalizer can be reasonably reduced. In another aspect, the voltage equalizer will provide superior reliability.
With reference to
With the central tap configuration, the second embodiment has the advantage of the reduced secondary windings 16, 17. In comparison to the first embodiment, the number of the secondary windings is reduced from 8 to 6.
In conclusion, the voltage equalizer in accordance with the present invention uses a single switch and a transformer to balance voltages among the series-connected battery units. The total number of electronic components is much fewer than that of inductor-based or capacitor-based voltage equalizers.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Number | Date | Country | Kind |
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100103228 | Jan 2011 | TW | national |